When a semiconductor device is tested by a semiconductor tester, the test is conducted by driving the semiconductor device with electric power from a power supply. When noise (noise components) is included in a constant voltage output from the power supply, it is difficult to accurately conduct the test. Accordingly, power supply noise reduction circuits for reducing noise included in a constant voltage output that is output from a power supply to a semiconductor device have been conventionally used in practice. These power supply noise reduction circuits are broadly divided into a passive low-pass filter that is formed only by passive components and an active low-pass filter that uses active components.
A passive filter is generally a combination of a bypass capacitor and a choke coil. The bypass capacitor is configured to include a capacitor (an AC shunt circuit) connected in parallel to a load and keeps an impedance of the capacitor no a noise signal at a low level to cause the capacitor to bypass a noise current, thereby suppressing a flow of noise into the load. Meanwhile, the choke coil is inserted in series to a power supply line extending from a constant voltage source to the load to prevent a passage of a noise current and further divides a noise voltage according to a ratio between a series impedance of the power supply line and a shunt impedance of the bypass capacitor to increase an impedance ratio, thereby enhancing a noise suppression effect to suppress noise application to the load.
While a filter circuit using an operational amplifier or the like is generally applied as an active filter for a constant voltage source, a constant-voltage stabilization circuit normally functions as a filter in a constant-voltage power supply circuit that handles a large amount of electric power. Furthermore, a filter circuit that is inserted into an electrical supply line outside a power supply device is generally a so-called dropper-type simple constant-voltage power supply circuit designed for DC voltage stabilization including voltage conversion accompanied by voltage drop and ripple removal, such as a three-terminal regulator or a shunt regulator, and can reduce noise as a second-order effect of the constant voltage stabilization accompanied by voltage drop.